Clusters of cognitive impairment among different phenotypes of myotonic dystrophy type 1 and type 2

Neuropsychological examinations in myotonic dystrophy (DM) patients show a great variability of results from a condition of intellectual disability to the subtle cognitive impairments. It is unclear if different clusters of neuropsychological deficits appear in different phenotypes of DM, or if there are patients with no cognitive deficit at all. The aim of this study is to assess cognitive impairments among patients with different phenotypes of DM type 1 (DM1) and type 2 (DM2), and to potentially define cognitive clusters in these disorders. Study comprised 101 DM1 and 46 DM2 adult patients who were genetically confirmed. Patients underwent analysis of five cognitive domains (visuospatial, executive, attention, memory and language). Virtually all DM1 patients had cognitive defect with approximately 2-3 cognitive domains affected. On the other hand, one-third of DM2 patients had completely normal neuropsychological findings, and in other two-thirds approximately 1-2 domains were affected. Cluster analysis showed that in both diseases visuospatial and executive dysfunctions seemed to be the main cognitive defects, while memory and language impairments appeared in more severe phenotypes. Our results showed that a single form of DM1 or DM2 may consist of several cognitive clusters. Understanding of cognitive impairments in DM is very important to follow positive and side effects in ongoing and future clinical trials.